This invention relates generally to dental instruments and, more particularly, to trays for obtaining an impression of a patient's dentition.
Dental trays for obtaining an impression of a patient's dentition are known. Such trays generally include a tray portion anatomically contoured to fit over at least a part of a patient's upper and/or lower dentition of which an impression is to be obtained. The tray portion is loaded with a suitable settable impression material and situated opposite to the desired dentition part whereupon the patient bites into the impression material to form an impression of the dentition in the material. After the impression material sets, it is used as a mold into which plaster can be poured which, upon setting, forms a model of the dentition.
A problem encountered in the use of conventional dental impression trays is that as and after the impression is taken and before the impression material has set, the impression material tends to move with respect to the wall or walls defining the tray portion. In particular, as the impression is being taken, the soft impression material tends to separate from the wall and move inwardly into the tray portion and also tends to spread laterally along the wall. Moreover, after the impression is taken, the impression material tends to lift out of the tray as the patient's teeth are removed from the impression material. Such movement of the impression material detracts from the precision of the impression obtained.
Attempts have been made to prevent the soft impression material from moving in the manner described above. For example, impression adhesives are available which are applied to the tray wall prior to the tray portion being loaded with impression material. However, these are not entirely satifactory as movement is not entirely eliminated and since an additional step is required in the impression procedure. In an impression tray available from Premier Dental Products Co. of Norristown, Pa., and illustrated in U.S. Pat. Nos. Des. 266,269 and 277,605, a series of vertically extending ribs are formed in the tray wall which at least to some extent inhibit lateral spreading of the impression material along the tray wall. However, the impression material still tends to separate from the wall and move inwardly into the tray as well as lift out of the tray when the teeth are removed from the impression material.